Research Of Resonant Converter Based Active Equalizer For Lithium-Ion Battery Pack

Due to the gradual depletion of traditional energy and the rapid development of new energy,lithium-ion battery packs are becoming widely used in electric vehicle(EV)and energy storage station(ESS).In the lithium-ion battery pack,the inconsistency between series connected battery cells will reduce the available capacity and service life of the battery pack.Therefore,battery equalizer in the battery management system(BMS)is needed to equalize the batteries.This paper introduces the research status of battery equalizer,uses LC series resonant circuit as energy carrier to improve the active equalizer,and proposes two novel resonant converter based active equalizers for the battery pack of EV and ESS.For the EV using new batteries with good consistency,a Groud Clamped LC Resonant Converter(GCLCC)based Direct Cell to Cell(DC2C)equalizer is proposed.By introducing an auxiliary switch and unique "groud clamped" switching state,this equalizer not only reduces the number of switches,but also realizes the bootstrap power supply for the driver circuit.On the basis of traditional DC2C equalizers,it further reduces the equalizer’s cost and volume.For the ESS using retired batteries with poor consistency,a Bipolar Resonant LC Converter(BRLCC)based Multi-Cell to Multi-Cell(MC2MC)equalizer is proposed.This equalizer features a symmetrical switch network,and can provide flexible,efficient and stable equalization modes by using the bipolar resonant switching states.On the basis of traditional MC2MC euqlizer,it greatly improved the equalization speed with same equalization efficiency.This paper analyzes the circuit structure and equalization principle of the above two active equalizers,completes the derivation of mathematical model,simulation verification,comparison with typical active equalizers,and also builds the experimental platforms for verification.The comparative analysis and experimental results verify the advantages and effectiveness of the proposed GCLCC equalizer and BRLCC equalizer.